1. Field of the Invention
The present invention relates to metal oxide doped cerium oxides and a method for the preparation thereof. Further, the present invention relates to a resin composition or a cosmetic composition in which said metal oxide doped cerium oxides or a complex composed of said metal oxide solid doped cerium oxides and an oxide are blended.
2. Description of the Prior Art
As is well known, ultra violet ray causes degradation of plastic resins, and many kinds of countermeasure are carried out to protect the degradation. As one of the countermeasure method, it is widely practiced that a plastic resin is admixed with an ultraviolet shielding agent including an organic ultra violet ray absorbing agent or an inorganic ultraviolet ray scattering agent. And by admixing these agents in plastic resin, the adverse influence of ultra violet ray is reduced. As the organic ultra violet ray absorbing agent, salicylic acid type compound, benizophenon type compound, benzotriazol type compound or cyanoacrylate type compound can be mentioned, however, recently, the lack of heat resistance, lack of durability to weather or the safety of decomposed chemicals of it are becoming serious problems. To solve these problems, fine particles of titanium dioxide or fine particles of zinc oxide which are the inorganic ultra violet ray scattering agent are developed, however, the lack of dispersability of these agents is a problem and the catalytic activity of these agent are becoming a new problem. Recently, especially regarding titanium dioxide, it is pointed out that the generation of singlet oxygen by photo catalyst function of it causes new problem.
Ultraviolet ray has an adverse influence also on living bodies. Namely, it is well-known that the so called UV-B ultraviolet ray in the wavelength range of 280 to 320 nm causes cutaneous inflammations such as erythemas blister and the like while the so called UV-A ultraviolet ray in the wavelength range 320 to 400 nm causes tanning of skin by the accelerated formation of melanin. As the countermeasure method against above mentioned adverse influences of the ultraviolet ray, many kinds of sunscreen cosmetic compositions have been developed hereto before. The ultraviolet shielding agents contained in conventional sunscreen cosmetic compositions can be grossly classified into two types including an ultraviolet absorbing agent such as cinnamic acid type, benzophenon type or dibenzoylmethane type and an ultraviolet scattering agent such as zinc oxide or titanium dioxide. However, above mentioned ultraviolet absorbing agents have several problems, such as low absorptivity of ultraviolet ray and safety when the admixing amount in a cosmetic composition is too high. Further, in a case of conventional ultraviolet scattering agent, since it is impossible to improve the transparency even if the (dispersibility of particles is improved, the admixing use of it not only causes the deterioration of feeling when the cosmetic composition is applied but also the skin look becomes unnatural. Recently, the use of cerium compound as an ultraviolet scattering agent has been proposed, for example, in Japanese Patent Laid Open Publication 6-145645 or Japanese Patent Laid Open Publication 7-207151. However, since cerium oxide has strong catalytic activity, it has a problem that accelerates the oxidation decomposition of resin or oil and causes color change and generates offensive odor when admixed in cosmetic compound or resin. Thereupon, the development, of new cerium compound which has a function as the ultraviolet scattering agent and does not have catalytic activity has been desired. And in Japanese Patent Laid Open Publication 9-118610, silica-cerium oxide composite particle is proposed, however, the reduction of catalytic activity of said silica-cerium oxide composite particle is almost accomplished but the ability for ultraviolet ray shielding is not sufficient.
The present invention is carried out concerning above mentioned circumstance, whose object is to provide metal oxide doped cerium oxides with strong ultraviolet ray shielding ability, lower catalytic activity and with excellent transparency. Further, the other object of this invention is to provide a composite composition of said metal oxide doped cerium oxides coated with metal oxide. Furthermore, the other object of this invention is to provide a resin composition or a cosmetic composition to which said metal oxide doped cerium oxides or a composite thereof is admixed with.
That is, the present invention is the metal oxide doped cerium oxides composed of cerium oxide in which metal ion having larger ion radius than that of tetravalent cerium ion (Ce4+) and/or lower valence metal ion than Ce4+ are doped. As the concrete example of a metal ion used in this doping, Ca2+, Y3+, La3+, Nd3+, Eu3+, Tb3+, Sm3+, Mg2+, Sr2+, Ba2+, Ce3+ and the like can be mentioned. The desirable cerium oxide concentration in said metal oxide solid doped cerium oxide is 40 to 98 molar %. Further, when the color index of said metal oxide doped cerium oxide is estimated by L*, a* and b* space, the desirable region of L* is larger than 80, the desirable region of a* is smaller than 4 by absolute value and desirable region of b* is smaller than 10 by absolute value, further the desirable average particle size is ultra fine particle of 2 to 4 nm.
Further the metal oxide doped cerium oxides of this invention can be prepared by following steps. That is, prepare the metal oxide doped cerium oxide at the temperature lower than 60xc2x0 C. and in the condition of pH higher than 5 by reacting aqueous solution of cerium salt, aqueous solution of metal ion having larger ion radius than that of Ce4+ and/or lower valence metal ion than Ce4+ and alkali, then by adding oxidizing agent in it at the temperature lower than 60xc2x0 C. Furthermore the metal oxide doped cerium oxide of this invention can be prepared by adding and mixing aqueous solution of cerium salt, aqueous solution of metal ion having larger ion radius than that of Ce4+ and/or lower valence metal ion than Ce4+, alkali and oxidizing agent simultaneously at the temperature lower than 60xc2x0 C. and in the condition of pH higher than 5.
The present invention also relates to a composite composition of said metal oxide doped cerium oxides coated by one or more kinds of oxide selected from the group composed of silicon oxide, zirconium oxide, aluminium oxide, iron oxide and titanium dioxide. Further, the present invention relates to the resin composition to which said metal oxide doped cerium oxide or the composite composition thereof is blended. Still further, the present invention relates to the cosmetic composition to which said metal oxide doped cerium oxide or the composite composition thereof is blended. The surface treated metal oxide doped cerium oxides or the composite composition thereof can be blended to the cosmetic composition. And, said cosmetic composition can contain an ultraviolet ray absorbing agent, and/or an ultraviolet ray scattering agent. As the desirable example of said ultraviolet ray absorbing agent, one or more kinds of compound selected from the group composed of oxybenzone, octyl metoxycinnamate and 4tertbutyl-4xe2x80x2-methoxy dibenzoylmethane can be mentioned, and the desirable contents of the ultraviolet ray absorbing agent is 0.1 to 40% by weight. As the desirable example of said ultraviolet ray scattering agent, titanium dioxide and/or zinc oxide can be mentioned, and the desirable contents of the ultraviolet ray scattering agent is 0.1 to 50% by weight. Above mentioned cosmetic composition is suited to be used as a sunscreen cosmetic composition.
The metal oxide doped cerium oxide of this invention is the cerium oxide in which metal ion having larger ion radius than that of Ce4+ and/or lower valence metal ion than Ce4+ are doped. By doping said metal ion, the catalytic activity of cerium oxide can be reduced Further, by doping said metal ion, the transparency of cerium oxide is improved and the ultraviolet ray shielding effect can be improved. As the concrete example of metal ion which has larger ion radius than Ce4+ (ion radius of Ce4+ is 0.097 nm), Ca2+, La3+, Nd3+, Eu3+, Tb3+, Sm3+, and Ce3+ can be mentioned. As the concrete example of metal ion which has lower valence than Ce4+, Y3+, Mg2+, Sr2+ and Ba2+ can be mentioned besides above mentioned metal ions. These metal ions can be used alone or together with. In addition, the desirable concentration of metal oxide doped cerium oxide is 40 to 98 molar %.
The metal oxide doped cerium oxide of this invention can be prepared by following steps. That is, prepare metal hydroxide doped cerium hydroxide, for example, at the temperature lower than 60xc2x0 C. and in the condition of pH higher than 5, by reacting aqueous solution of cerium salt, aqueous solution of metal ion having larger ion radius than that of Ce4+ and/or lower valence metal ion than Ce4+ and alkali, then add oxidizing agent in it maintaining the temperature lower than 60xc2x0 C. The obtained reacted product is rinsed by water, filtered, and dried or calcined then pulverized. Thus the metal oxide doped cerium oxide can be obtained. As the concrete example for the preparation of said solid solution of cerium hydroxide and metal hydroxide following methods can be mentioned. That is, (1) the method to add aqueous solution of cerium salt and aqueous solution of salt of metal to be solid solved simultaneously into a container in which alkaline solution is contained, or (2) the method to add aqueous solution of cerium salt, alkaline solution and aqueous solution of salt of metal to be solid solved simultaneously into a container in which water is contained.
Furthermore the metal oxide doped cerium oxide of this invention can be prepared by adding and mixing aqueous solution of cerium salt, aqueous solution of metal ion having larger ion radius than that of Ce4+ and/or lower valence metal ion than Ce4+, alkali and oxidizing agent simultaneously. For instance, at the temperature lower than 60xc2x0 C. and in the condition of pH higher than 5, aqueous solution of cerium salt, aqueous solution of salt of metal to be solid solved, alkaline solution and hydrogen peroxide which is an oxidizing agent are added simultaneously into a container in which water is contained. The obtained reacted product, is rinsed by water and filtered, dried or calcined then pulverized, thus the fine particles of metal oxide doped cerium oxide can be prepared.
Aqueous solution of cerium salt which is used in above mentioned reaction, can be prepared by solving e.g. cerium carbonate in aqueous solution of hydrochloric acid or nitric acid, or by solving cerium chloride, cerium nitrate, cerium sulfate or cerium acetate in water. As alkali, aqueous solution of alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or aqueous solution of ammonia can be used. Further, as the salt of metal to be doped, for example, chloride, salt, of nitric acid, salt of sulfuric acid or salt of acetic acid can be mentioned. As the oxidizing agent, hydrogen peroxide, hypochlorous acid, sodium hypoclilorite, potassium hypochlorite, calcium hypochlorite and ozone can be used. In above mentioned methods, the doping is carried out in aqueous solution, however not limited with these examples.
In any kind of above mentioned reacting method, nano-size particles of metal oxide doped cerium oxide having 2-4 nm average diameter can be obtained by keeping the temperature of solution lower than 60xc2x0 C., desirably lower than 40xc2x0 C. and by rising pH higher than 5 during the adding process of oxidizing agent. Such kind of fine pulverized particles of metal oxide doped cerium oxide have a superior transparency at visible ray range and have an excellent dispersability, further, have a good ultraviolet ray shielding effect.
Further, in any kind of above mentioned reacting method, the yellowish tendency of metal oxide doped cerium oxide can be moderated and the white particles are obtained. And when the color index is estimated by L*, a* and b* space, the metal oxide doped cerium oxide whose L* is larger than 80, a* is smaller than 4 by absolute value and b* is smaller than 10 by absolute value can be obtained. In this invention, the term of L*, a* and b* space is regulated by CIE1976L* a* b* color space which is authorized by CIE (Commission Internationale de Enluminure) on 1976. This color space is a coordinate having axis of L*, a* and b* which are regulated by following numerical formulae.
xe2x80x83L*=116(Y/Y0)⅓xe2x88x9216
a*=500[(X/X0)⅓xe2x88x92(Y/Y0)⅓]
b*=200[(Y/Y0)⅓xe2x88x92(Z/Z0)⅓]
(wherein, X/X0, Y/Y0, Z/Z0 greater than 0.008856, X,Y and Z indicate 3 stimulate values of object color, X0, Y0 and Z0 indicate 3 stimulate values of color source which illuminates the object, and standardized to Y0=100).
In the present invention, color index estimated by L*, a* and b* space is settled to L*xe2x89xa780, |a*|xe2x89xa64, |b*|xe2x89xa610. And each L*, a* and b* value are measured by color difference meter (product of Nihon Denshoku Kogyo).
Said metal oxide doped cerium oxide of this invention can be used as the composite form, namely coated with oxide (hereinafter said composite can be expressed as xe2x80x9coxide coated metal oxide doped cerium oxidexe2x80x9d). As the oxide to be used for the preparation of said oxide coated metal oxide doped cerium oxide, one or more kinds of compound selected from the group composed of silicon oxide, zirconium oxide, aluminum oxide, iron oxide and titanium dioxide. By the use of composite of metal oxide doped cerium oxide which is coated with oxide, the catalytic activity can be more weakened and the dispersability can be improved.
The oxide coated metal oxide doped cerium oxide can be prepared by the further treatment of metal oxide doped cerium oxide prepared by the use of afore mentioned starting materials and by afore mentioned method with said oxide. For example, aqueous solution of cerium salt, aqueous solution of salt of metal to be doped (e.g. salt of calcium) and aqueous solution of alkali are added into water which is kept at the temperature lower than 60xc2x0 C. and higher than pH 9, then calcium hydroxide doped cerium hydroxide can be obtained. An oxidizing agent such as hydrogen peroxide is further added to generate calcium oxide doped cerium oxide. Then heated to the temperature higher than 80xc2x0 C. and keeping pH higher than 9, aqueous solution of sodium silicate and aqueous solution of mineral acid such as hydrochloric acid, nitric acid or sulfuric acid are added to coat silicon oxide over calcium oxide doped cerium oxide, and rinsed by water, filtrated, dried, calcined and pulverized. Thus the silicon oxide coated calcium oxide doped cerium oxide can be obtained. In this case, desirable amount, of sodium silicate to be added is 2 to 60% by weight, to coat subject of solid solution as SiO2. Also in this case, by keeping pH of solution under 8 at the finishing point of oxidation, the yellowish tendency of oxide coated metal oxide doped cerium oxide can be weakened and improve the color index, and the metal oxide doped cerium oxide whose L* value is bigger than 80, absolute value of a* is smaller than 4 and absolute value of b* is smaller than 10 when color index is estimated by L* a* and b* space can be obtained. Further, by keeping pH of solution higher than 5 during oxidizing agent adding process, ultra fine particles of silicon oxide coated calcium oxide doped cerium oxide whose average particle diameter is 2 to 4 nm can be obtained.